The present invention relates to a method for punching-shearing a bulge formed during a process for pressure butt welding of steel members such as reinforcing bars for the purpose of inspecting the quality of the butt welded joint.
Pressure butt welding of steel members is effected, as widely known to the art, by utilization of either gas heating or electric heating. In the case of the gas pressure butt welding of steel members, pressure is exerted on the steel members toward the butted portions thereof with the butted portions heated by burning gas, thereby expanding the metal (steel) of the heated portions outwardly to form a bulge of a sufficient size around the joint portion and obtaining a welded joint exhibiting given strength. In the case of the electric pressure butt welding of steel members, the steel members are clamped by electrodes, and pressure is exerted on the steel members in the same manner as in the gas pressure butt welding with the heating of the butted portions facilitated by electric resistance due to the flow of electric current, thereby forming a bulge around the joint portion.
Since it is a well-established concept in this field that the strength of the welded joint is enhanced by increasing the cross sectional area of the joint portion, the welded joint is put to practical use in the state wherein the bulge formed during the pressure butt welding process still remains around the joint portion.
To inspect the quality of the butt welded joint, there have heretofore been adopted a fracture testing method on the basis of sampling inspection because of impossibility of determining whether or not the welding is completely effected from the appearance of the surface of the bulge. However, this fracture testing method lacks in reliability when it is desired to inspect the precise state of welding. For this reason, there have also been adopted an ultrasonic flaw detecting method without fracturing any portion in the vicinity of the joint portion. Although this detecting method is advantageous for detecting considerable defects in the welded joint such as existence of unwelded portions in the joint portion due to partial oxidization, presence of surface cracks resulting from superfusion, etc., it entails impossibility of detecting a frequently experienced defect in the welded joint when fractured, which defect is the formation of brittle flat fracture because of the presence of oxides, sulfides, etc. of various sizes in the vicinity of the joint portion in a dispersed state, and has difficulty in detecting the entire surface of the joint portion.